The present invention is related to the field of audio signal processing and more specifically to techniques for transmitting and recovering one-dimensional signals.
The association of audio with graphic images creates a rich multi-media experience. Typically multi-media creation or playback requires a computer and other sophisticated and expensive electronic equipment. The audio portion is either a digital file which is stored on a CD or disk or an analog signal encoded on magnetic tape.
Often, however, graphic images are printed and saved on paper which is then stored in files or albums. There is no currently existing technique for easily associating audio with these printed graphic images.
Various techniques for transferring information characterizing an audio signal to paper have been developed. All of these techniques have been intended for examination and analysis of the audio waveform or spectrum, rather than for reproduction of the sound. For example, spectrographs for displaying time domain information as frequency domain information on an analog medium are well known. Originally implemented as analog devices, spectographs were utilized to record spectograms on special paper using a spinning drum. These devices were disadvantageous for a number of reasons, including poor resolution and the requirement for a special paper type. While digital spectographs have been implemented, the images or spectrograms produced by digital spectographs are such that the original information is unrecoverable from the spectograms.
Other devices such as a “Pattern Playback” convert spectrographic pictures (voice prints) into sound signals. The pictures can be synthetic patterns that are painted by hand, or photographic copies of actual spectrograms. The Pattern Playback use a tone wheel for providing the first 50 harmonics of a fundamental frequency of 120 Hz, therefore providing a frequency range of 0 Hz to 6 KHz. Disadvantageously, the device speaks only in a monotone due to the fixed fundamental frequency. Additional information regarding pattern playback is obtainable at the following URL: http://www.haskins.yale.edu/MISC/PP/pp.html.
Further yet, other devices have been described that take an image as an input (for example, formant or sinusoidal trajectories) and generate a signal as an output. However, no practical technique is described for converting audio into an image.
Another prior art encoding technique is helical scanning, used for example in VCRs. In this case, the 1D signal is represented in the 2D medium as a series of strips, each representing a window of time. For example, consider the case where the 1D signal is an audio waveform and that the windows are printed vertically on the page with adjacent windows proceeding horizontally. To reconstruct the 1D signal, one simply reads a vertical strip, and at its end, moves to the next horizontal strip. Note that while the 2D signal is vertically continuous, it is not horizontally continuous. Moving horizontally one will encounter discrete, unrelated values as each strip number is traversed. Accordingly, there must be a provision to register with the new strip in order to obtain accurate results.
There is also a prior art “digital” technique which encodes signals onto an image. But this technique is designed purely for digital signals, and includes substantial error correction and detection to ensure the absence of noise in the transmitted signal. It also uses discontinuous imaging—the image is made up of individual dots, each of which conveys discrete information. Additional information on this technique is available at the following URL: http://www.intacta.com. Such a discrete system requires accurate registration because the system must be able to determine whether the area being scanned represents one of two binary values. If the scanner views the edge of a dot the information is meaningless because it is not possible to determine which of the binary values is encoded.
Accordingly, there does not currently exist a practical and efficient technique for transmitting audio/voice signals on paper or other media having graphic content so that the audio/voice can be associated with graphic content.